Cannot establish SSH session: kex error : no match for method mac algo client

[ericg]

Hey,

Hope you're having a good day, and I thank you for stopping by to read my post.

I've run into this new issue as of late, I have this ssh check that I was performing on hosts via a Zabbix Proxy 6.0.29 on Ubuntu 22.04 that was working successfully. However I recently deployed two new proxies running Zabbix Proxy 6.0.33 on Ubuntu 24.04 and am now getting the error:
Cannot establish SSH session: kex error : no match for method mac algo client->server: server [hmac-sha1,hmac-md5], client [[email protected],[email protected],hmac-sha2-256,hmac-sha2-512]

I've looked into Zabbix's ssh.run command and came up with this: ssh.run[MACs,{HOST.IP},,,"MACs=hmac-sha1,hmac-md5"] as a potential solution, but it doesn't work and returns the same error.
I've also tried installing other libssh libraries as well, and I tried removing all libssh libraries and installing libssh2-1 from Ubuntu 22.04, but that causes the Zabbix Proxy to fail and will no longer start; which is understandable since I'm sure the original package I installed is looking for the libssh-4 package it installs with the Zabbix Proxy.

Beyond the idea that older MAC protocols simply aren't supported with libssh-4 I'm at a loss as to what I can do to resolve this.
If anyone can assist me I would greatly appreciate it.

[ericg]

Answered my own question.

Resolution
Turns out that /etc/ssh/ssh_config governs the libssh-4 library even for Zabbix. So if you simply just uncomment the MACs line it will fix you problem, at least on Ubuntu 24.04.
Your MACs line should be like this: MACs hmac-md5,hmac-sha1,[email protected]


Thank you to anyone who read this post and took the time to consider my issue. I hope the resolution I've provided can help someone else some day